Portable lighting device

ABSTRACT

A method for controlling a portable lighting device. The device has a switched-mode power supply, a light source, a high frequency switch, a controller controlling the operation of the light source and a user interface for inputting commands to the controller. A DC power source has a negative pole that is connected by only one single electric contact with the lighting device tail. The method for controlling a portable lighting device includes connecting a DC power source, an inductor, a light source, a high frequency switch and a resistor in series, measuring a voltage across the resistor, and controlling the high frequency switch dependent on the voltage measured across the resistor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. Ser. No.15/244,776, filed on Aug. 23, 2016, which itself is a continuation ofU.S. Ser. No. 14/541,847, filed on Nov. 14, 2014, which itself was acontinuation application of U.S. Ser. No. 14/184,190, filed on Feb. 19,2014, which itself was a continuation application of U.S. Ser. No.13/216,092, filed on Aug. 23, 2011, the disclosures of which are herebyspecifically incorporated herein by reference in their entireties.

TECHNICAL FIELD OF THE INVENTION

The current inventions generally relate to the field of portablelighting devices, including, for example, flashlights, lanterns andheadlamps, and their circuitry.

BACKGROUND OF THE INVENTION

Various hand held or portable lighting devices, including flashlights,are known in the art. Such lighting devices typically include one ormore dry cell batteries or rechargeable batteries having positive andnegative electrodes. The batteries are arranged electrically in seriesor parallel in a battery compartment or housing. The battery compartmentcontains the batteries and may also, in some instances, be used to holdthe lighting device. An electrical circuit is established from a batteryelectrode or terminal through conductive means which are electricallycoupled with a light source, such as a lamp bulb or a light emittingdiode (“LED”). After passing through the light source, the electriccircuit continues through conductive means that are electrically coupledto the light source, which in turn are in electrical contact with theother electrode or terminal of a battery. The circuit includes a switchto open or close the circuit. Actuation of the switch to close theelectrical circuit enables current to pass through the lamp bulb, LED,or other light source and through the filament, in the case of anincandescent lamp bulb—thereby generating light.

It may be desirable to provide multiple modes of operation for differentneeds. For example, in addition to the normal “full power” or “standardpower” mode, a momentary mode only keeping the flashlight on as long asa pushbutton is pushed by a user, and/or a blink mode providing a strobelight or a blinking in a certain sequence like an SOS mode can beimplemented in a portable lighting device, such as a flashlight. In sucha portable lighting device, the user selects the desired mode ofoperation by manipulation of a user interface, which can be a mainswitch. For example, when the portable lighting device is in the normalmode or the power save mode of operation, the portable lighting devicemay be transitioned to another mode of operation, such as an SOS mode,by manipulating the main switch to momentarily turn “off” and then turnback “on” the portable lighting device. In another lighting device, themain switch may be required to be depressed and held a certain period oftime to cause the lighting device to index to the next operational mode.Another option might be multiple pressing of the main switch by a userwithin a certain time between pressing and releasing the main switchbutton. A portable lighting device that includes advanced functionalitymay also include an electronic power switch controlled by amicrocontroller or microprocessor to provide the desired functionality.

Flashlights and other portable lighting devices have conventionallyemployed a mechanical power switch in the main power circuit of theflashlight to turn “on” and turn “off” the portable lighting device.When the user turns “on” the portable lighting device, the usertypically presses down or otherwise manipulates the mechanical powerswitch to mechanically connect two contacts to close the switch andcomplete the power circuit, thereby allowing current to flow from thepositive terminal of the batteries, through the light source and to thenegative terminal of the batteries. When the user turns “off” theportable lighting device, the user again manipulates the mechanicalswitch to disconnect the two contacts of the switch and thereby open theswitch and break the power circuit. The mechanical power circuit in suchdevices, therefore, acts as a conductor in completing the power circuit,and thus conducts current throughout the operation of the portablelighting device.

For example, in multi-mode electronic portable lighting devices, thevarious modes of operation may be selected by a user turning off thelighting device for less than a predetermined period of time, such as 1to 2 seconds, and then turning the lighting device back on again. Inresponse to this short turn off period, the lighting device indexes tothe next mode.

A known design for flashlights is to divide the electrical circuit sothat the circuit elements needed in the direct vicinity of the lightsource are provided in the head of the flashlight, while the parts ofthe circuit that belong to the control of the flashlight areaccommodated in the tail of the flashlight, including the man-machineinterface, for instance a pushbutton.

Typically, at least 2 circuits are necessary, namely the main powersupply circuit providing electrical power to the light source and acontrol circuit that controls the electrical power supplied to the lightsource. For any light source, specifically if the light source is anLED, the current through the LED needs to be constant or at leastsomewhat constant to provide a relatively constant output of light. Inaddition, it may be desirable to adjust the current so that theelectrical power consumed by the LED stays constant to the extent thisis desired. For instance, it may sometimes be desirable to accept aminor drop in electrical power, indicating to the user that the batteryis getting old rather than regulating the buck circuit such as tocompensate in full for the drop in electrical energy and then have aflashlight shut down without any warning at some point in time.

Regulation is typically achieved by a well known buck converter thatreduces the voltage from the DC power source to the voltage needed foroperating the LED, for instance to reduce a battery voltage of 5 V to anLED operating voltage of 3.2V. Buck converters comprise a high frequencyswitch, for instance turning the battery power periodically on and offat a frequency of 600 kHz. The regulating performance is achieved by apulse width modulation (PWM), meaning that the duty cycle of the highfrequency switch is modulated by modulating the time during which theswitch is closed in comparison to the time over which the switch is openover one opening-closing cycle of the switch. Opening and closing theswitch is repeated periodically at a high frequency, for instance 600kHz. During the time the high frequency switch is closed, an inductor ischarged that is connected in series with the light source, and duringthe time the high frequency switch is closed the inductor dischargeselectrical energy through the light source.

For controlling the duty cycle, typically a control circuit including aDC to DC converter circuit and/or a microcontroller is provided and thecurrent through the light source is measured and sent as an input signalinto the microcontroller that controls directly the duty cycle of thehigh frequency switch. In a flashlight, this results in a variety ofdesign problems, for instance:

1. The man-machine interface is located in the tail. Therefore, it ispreferred to provide also the microcontroller in the tail. Otherwise, anelectric circuit would be necessary for transmitting the commands fromthe user through a tail switch to wherever the microcontroller isprovided within the flashlight.

2. The control circuit needs to be provided with power. When providingthe control circuit in the tail of the flashlight, while the lightsource needs to be of course in the head of the flashlight, differentelectric circuits are needed, i.e. the battery power needs to be broughtboth to the head and to the tail. This requires relatively complexmechanical parts like spring probes, contacts, and a housing able toaccommodate these parts. Also, it makes the flashlights less robust asthe risk of failure generally rises the more parts and the moreelectrical contacts need to be functional.

3. Since the LED is in the head of the flashlight, it is not onlydifficult to measure the current through the LED in the head whererelatively little space is provided, but it would also require stillanother circuit to send this signal back into the DC to DC converterand/or microcontroller in the tail of the flashlight.

The result in the prior art was to provide several spring probes thatcontact different contacts. Since only one spring probe can be alignedwith the central axis of the portable lighting device, contact ringsneed to be provided that can be contacted by biasing the spring probesagainst these contact rings. For using standard batteries, one solutionin the prior art was to provide a battery cassette and provide contactrings on the battery cassette, and to provide contact rings in the headand the tail of the flashlight that can be contacted by spring probesprovided in the battery cassette. While this solution works reliably, itcomes at the price of a more complex design and is not a preferredsolution for heavy duty portable lighting devices such as in use by lawenforcement and the military favoring simple designs.

SUMMARY OF THE INVENTION

One object of the present patent document is to provide an improvedportable lighting device that addresses or at least ameliorates one ormore of the foregoing problems or needs. To this end, a number ofportable lighting devices and methods of operating same are describedherein. In general, the portable lighting devices may be any type ofportable lighting device, including, for example, flashlights,headlamps, lanterns, etc.

In one aspect, a lighting device is provided comprising a switched-modepower supply comprising a high frequency switch that is switched at aswitching frequency; a lighting device head accommodating a lightsource; a lighting device tail accommodating at least a user interfacefor inputting commands to the controller; a controller regulating thecurrent through the light source; an electric conductor connecting thelight source in the lighting device head with the user interface in thelighting device tail; and a DC power source having a negative pole thatis connected by only one single electric contact with the lightingdevice tail.

Another aspect of a potential method of operating a portable lightingdevice, such as a flashlight or headlamp, involves a method forcontrolling a portable lighting device, comprising: electricallyconnecting in series in the subsequent order a) a DC power source, b) aninductor, c) a light source, d) a high frequency switch and e) aresistor; measuring a voltage across the resistor; and controlling thehigh frequency switch dependent on the voltage measured across theresistor.

Further aspects, objects, and desirable features, and advantages of theinvention will be better understood from the following descriptionconsidered in connection with the accompanying drawings in which variousembodiments of the disclosed invention are illustrated by way ofexample. It is to be expressly understood, however, that the drawingsare for the purpose of illustration only and are not intended as adefinition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit block diagram of the buck converter circuitaccording to the invention.

FIG. 2 is a circuit block diagram of the buck converter circuitaccording to the invention in connection with a control circuitaccording to the present invention.

FIG. 3 is a plan view of an exemplary flashlight according to theinvention.

FIG. 4 is a cross-sectional view of the flashlight of FIG. 3 taken alongthe plane indicated by Line B-B.

FIG. 5 is a plan view of a spacer placed between 2 batteries connectedin series.

FIG. 6 is a cross-sectional view of the spacer of FIG. 5 taken along theplane indicated by Line C-C.

FIG. 7 is a user interface flow chart demonstrating an exemplaryembodiment of various operational modes for a flashlight.

FIG. 8a is a user interface flow chart demonstrating the exemplaryembodiment of FIG. 7 starting at a momentary mode of the flashlight.

FIG. 8b is a control circuit flow chart demonstrating the exemplaryembodiment of FIG. 7 starting at a momentary mode of the flashlight.

FIG. 9a is a user interface flow chart demonstrating the exemplaryembodiment of FIG. 7 starting at a latch mode of the flashlight.

FIG. 9b is a control circuit flow chart demonstrating the exemplaryembodiment of FIG. 7 starting at a latch mode of the flashlight.

FIG. 10a is a user interface flow chart demonstrating the exemplaryembodiment of FIG. 7 starting at a strobe mode of the flashlight.

FIG. 10b is a control circuit flow chart demonstrating the exemplaryembodiment of FIG. 7 starting at a strobe mode of the flashlight.

FIG. 11 is a plan view of an exemplary flashlight according to the priorart.

FIG. 12 is a cross-sectional view of the flashlight of FIG. 11 takenalong the plane indicated by Line A-A.

FIG. 13 is a circuit block diagram of a buck converter circuit accordingto the prior art.

DETAILED DESCRIPTION OF THE DRAWINGS

Embodiments will now be described with reference to the drawings. Tofacilitate the description, any reference numeral representing anelement in one figure will represent the same element in any otherfigure. Further, in the following description, references to the front,forward, forward facing side or head end of a component shall generallymean the side of the component that faces toward the front end of theflashlight or other portable lighting device. Similarly, references tothe aft, back, rear, rearward facing side or tail end of a componentshall generally mean the side of the component facing the rear of theportable lighting device, e.g., the direction in which the tailcap islocated in the case of a flashlight.

FIG. 11 shows an exemplary prior art portable lighting device, in thefollowing called flashlight 1. Some distinct features and aspects inthis prior art device are incorporated also in the portable lightingdevice of the present invention. While these distinct aspects have allbeen incorporated into flashlights in various combinations, the scope ofthe present invention is not restricted to flashlights. Rather, thepresent invention is directed to each of the inventive features offlashlights described below both individually as well as in variouscombinations. Further, as will become apparent to those skilled in theart after reviewing the present disclosure, one or more aspects of thepresent invention may also be incorporated into other portable lightingdevices, including, for example, head lamps and lanterns.

The exemplary flashlight 1 according to FIG. 11 generally includesbarrel 2, head assembly 3 located at the forward end of barrel 2, andswitch and tailcap assembly 4 located at the rear end of barrel 2. Thehead assembly 3 is disposed about the forward end of the barrel 2, andthe switch and tailcap assembly 4 encloses the aft end of barrel 2.

The barrel 2 may include a textured surface along a portion of itslength for a user to grip. In the present embodiment, textured surfacemay be provided by broaching. Alternatively, textured surface maycomprise a knurled or machine surface. Any desired pattern may be usedfor textured surface.

FIG. 12 is a partial cross-sectional view of flashlight 1 of FIG. 1taken along the plane indicated by line A-A. A light source 6 is mountedto the forward end of the barrel 2. A battery cassette 7 is accommodatedwithin the barrel 2 and holds several batteries, for instance size AAAbatteries. The switch and tailcap assembly 4 comprises a circuit board 8holding a control circuit for controlling the power supply to the lightsource 6 and also for controlling various modes of operation for theflashlight if the specific flashlight is designed as a multi-modeflashlight. A man-machine interface MMI is provided in the form of atailcap pushbutton 9 allowing an input by the user by pressing thepushbutton 9, for instance to allow providing an input signal into thecontrol circuit on the circuit board 8.

For providing battery power on the one hand to the light source 6, onthe other hand to the control circuit implemented on the circuit board 8in the tailcap, a number of contacts and related spring probes 10 areprovided. Three spring probes 10 are provided in the switch and tailcapassembly 4 and one spring probe 11 is provided in the battery cassette 7for grounding a shoulder ring electrically connected to the light sourceso as to allow current to flow from a battery cassette contact 13through the LED light source 6 through the spring probe 11 into theswitch and tailcap assembly 4 where the control circuit and a highfrequency switch are provided for controlling the power circuit poweringthe LED light source. It is to be understood that each spring probecontacts 2 electrical contacts, namely one on each end of the springprobe. Four spring probes means that also in total 8 electrical contactsneed to be provided that may be subject to corrosion depending on theenvironment where the flashlight is used or whether the flashlight isused with care, for instance kept closed.

While this prior art flashlight has been successfully on the market forsome time and proven to work reliably, it becomes apparent that itrequires relatively complex component parts like the battery cassette 7allowing to accommodate 3 batteries and the additional spring probe 11to provide several contacts, a complex switch and tailcap assemblyhousing 14 that allows to accommodate 3 spring probes 10, and of coursethe in total 4 spring probes itself. It is noted that some of thiscomplexity arises from the fact that the LED light source is provided inthe head of the flashlight, while the control circuit including theman-machine interface is provided in the tail of the flashlight. Anobject of the invention is to keep these generally favorable locationsof the LED light source and the control circuit, but simplify thecomplexity of the design and consequently make it more robust,particularly to reduce the number of contacts and spring probes.

Before going into deeper detail with regard to the actual mechanicaldesign of the flashlight according to the present invention, first thecircuit according to the present invention is explained.

Light sources require typically a specific voltage and/or a specificcurrent. Particularly when light emitting diodes (LEDs) are used aslight sources, these require a regulated current source. However,portable DC power sources like batteries or rechargeable batteries asused in portable lighting devices such as flashlights are subject to achange in output voltage over time. These changes might occur due topartial discharging or other environmental influences like thetemperature of the environment in which the flashlight is used. Oneenergy efficient way of controlling the flashlight is the use ofso-called buck converters. A DC power source is used providing morevoltage than needed across the light source, and the control isperformed by a high frequency switch that is controlled by amicrocontroller to regulate the current through the light source.Specifically, the duty cycle is controlled, defined as the ratio betweena pulse duration and the period of a rectangular waveform. In otherwords, the high frequency switch is periodically opened and closed, andthe duty cycle is the ratio between the duration over which the switchis closed and the time period it takes to complete an entire cycle ofopening and closing of the switch. A duty cycle of 100% means that theswitch would be permanently closed, and a duty cycle of 0% means thatthe switch would be permanently open. The practical application, a dutycycle in between is chosen, for instance 60% meaning that the switch isclosed 60% of the time while the switch is open 40% of the time. Keepingthe switch closed over a longer time period means connecting the batterypower for a longer time period to the circuit, i.e. allows more batterypower to discharge into the circuit.

FIG. 13 shows a typical prior art buck converter. A battery 15 suppliesDC current at a voltage Vi. A high frequency switch 16 opens and closesat a frequency of for instance 600 kHz. When closed, electric currentcan flow through the outer circuit from the battery 16 through aninductor 17 into the LED 18 and from there back into the ground or intothe negative pole of the battery 15. The inductor 17 resists over acertain time period this current flow by storing electric energy in theform of a magnetic field, meaning that some voltage drops across theinductor while the remaining voltage drops across the LED 18 so thatsome voltage across the inductor plus the voltage across the LED equalsthe battery voltage. When the switch 16 is opened, the outer circuit isinterrupted, allowing the inductor 17 to discharge and maintain acurrent across the LED 18 via an inner circuit formed by the inductor17, the LED 18 and the diode 19 which three elements 17, 18, 19 are nowconnected in series in this inner circuit.

Returning to the closed state of the switch 16, if theoretically theswitch 16 would be kept closed for a long time and assuming an idealinductor not having any resistance, the voltage across the LED wouldfinally equal the battery voltage since the inductor will have finallycreated a stable magnetic field that is just determined by the finalcurrent that is the result of the battery voltage and the resistance ofthe LED and therefore will not store additional electric energy in formof a magnetic field. This explains why the average current through theLED can be controlled by controlling for how long the switch is closedduring one opening and closing cycle, i.e. by controlling the dutycycle. Since the average current through the LED is what matters as acontrolled variable, typically this current is measured as a feedbacksignal and provided as an input signal into the microcontroller thatcontrols the duty cycle.

For a flashlight, this creates 3 challenges:

1. The LED is located in the head of the flashlight and the currentthrough the LED is difficult to measure in this location.

2. Since the microcontroller is provided in the tail of the flashlight,it is difficult to transmit the measured current through the LED as asignal to the tail and would require an extra signal line.

3. As this typical buck converter topography shows, the switch istypically provided between the battery and the inductor that isconnected in series with the LED. In a flashlight, however, the batteryis provided in the barrel between the switch in the tail and the LED inthe head, so that the typical buck converter circuit as shown in FIG. 13is difficult to apply to a flashlight.

FIG. 1 shows the buck circuit topography according to the presentinvention. In interrupted lines, it has been indicated which particularparts of this circuit are located at which particular specific locationwithin the flashlight. The three major groups of the circuit are thehead circuit section 20, the barrel circuit section 21, and the tailcircuit section 22.

Using the same reference numerals as in FIG. 13, the head circuitsection 20 comprises the inductor 17 connected in series with the LED 18and the diode 19 connected in series with the LED 18. In FIG. 13, thiscircuit having the inductor 17, LED 18 and the diode 19 connected inseries was also called the inner circuit. Current through this innercircuit flows only when the high frequency switch 16 assumes its openposition.

The barrel circuit section 21 comprises the batteries, for instance two3 V batteries connected in series, and comprises the barrel 2 itselfhaving besides the function of mechanically holding the batteries 15also the function of a conductor that connects the light emitting diode18 with the high frequency switch 16. The barrel circuit section 21 canalso be described as the circuit section that connects the head circuitsection 20 with the tail circuit section 22.

The tail circuit section 22 comprises the high frequency switch 16 and aresistor 23. It also comprises a spring probe 24 that will be shown inits mechanical implementation in FIGS. 3 and 4. This spring probe 24 isin contact with the negative pole of the battery and is grounded. A node25 is provided between the high frequency switch and the resistor 23 formeasuring a voltage across the resistor. It is to be understood that theresistor provides only a minor resistance since its main purpose is justto allow calculating the battery power as the variable to be determinedbased on the measure voltage and the known resistance based on Ohm'slaw. Referring back to prior art FIG. 13 and its description, thebattery current is the current flowing through the outer circuit whenthe high frequency switch is in its closed position.

It becomes apparent that this circuit design as shown in FIG. 1 deviatesfrom the typical buck converter design shown in the prior art. Reasonsare that there are some design necessities or strong design preferenceswhere some component parts should be located within the flashlight, e.g.the LED in the head of the flashlight, the power source somewhere in themiddle, and the control including the MMI in form of the pushbutton inthe tail of the flashlight. This resulted not only in positioning thecomponent parts at different locations within the flashlight, butactually in an inventive reversed order in which these parts areconnected within the buck circuit topography.

Another inventive difference to prior art bucking circuits is that thecontrolled variable, i.e. the current through the LED, is not measured.As discussed above, measuring this voltage is difficult at the front ofthe flashlight and even if measured there as a feedback signal, suchsignal would somehow need to be conveyed into the tail of the flashlightwhere the control circuit is located. The invention therefore measures adifferent variable, namely the voltage at the resistor 23 at node 25.The resistor 23 is provided for that reason, and as can be seen bycomparing the circuit according to the invention as shown in FIGS. 1 and2 with the prior art circuit in FIG. 13, providing this resistor 23 inthe bucking circuit also deviates from the prior art.

Notably, the controlled variable, namely the current through the LED 18,is not measured at all, but instead the battery current is calculatedfrom the voltage across the resistor 23, and this battery current is fedinto the microcontroller to adjust the duty cycle by pulse widthmodulation, and only indirectly by regulating the battery current by theduty cycle, the voltage across the diode is regulated.

When the high frequency switch 16 is closed, current rises through thesystem (including the LED 18) and energy is stored in the inductor 17.When the high frequency switch 16 opens, the energy in the inductor 17is released through the LED and circulates back through the diode 19.The average LED current is the sum of the battery current when the highfrequency switch 16 is closed and the recirculating current when thehigh frequency switch 16 is open divided by the period of the PWMsignal. This means that the LED current is at least over major parts ofthe opening-closing cycle of the high frequency switch 16 higher thanthe battery current and is related to the duty cycle of the PWM. Thevoltage across the LED 18 floats to the necessary voltage for thecurrent passing through the LED 18, and the remaining battery voltage isimpressed across the inductor 17.

The LED current can be approximated by estimating the recirculatingcurrent and adding it to the battery current (measured at R1). Therecirculating current changes with a dropping battery voltage over time.The unique regulating method and circuit according to the inventionperform even without measurement of battery voltage by regulating thebattery current and therefore by indirectly regulating the LEDoperation. Regulating the battery current sets the initial powerdelivered to the LED and as the battery voltage gradually drops overtime, the power delivered to the LED drops. This method allows a simplecontrol circuit to effectively operate a LED in a series configuration.

The table 1 below shows calculations of power delivered to a typicalwhite LED (Cree XPG) using this method:

BATTERY CURRENT LED TYP LED VBAT (REGULATED) INPUT POWER EFF POWER VFCURRENT 5.50 1.00 5.50 0.80 4.40 3.20 1.38 5.00 1.00 5.00 0.80 4.00 3.201.25 4.50 1.00 4.50 0.80 3.60 3.20 1.13 4.00 1.00 4.00 0.80 3.20 3.201.00

In connection with FIG. 1 the buck converter circuit 26 has beendescribed. In the following, the control circuit 27 is described byreferring to FIG. 1, and how it interacts with the buck convertercircuit 26. As already discussed in connection with FIG. 1, a voltageacross the resistor 23 is measured at node 25. Through a signal line 28the measured voltage is transmitted into the microcontroller 29comprising an output signal line 30 that is directly connected with thehigh frequency switch 16. As discussed in connection with FIG. 2, thehigh-frequency switch 16 controls the duty cycle and this controls thebattery current flowing through the outer circuit of the buck converter.

It is to be noted that the control circuit 27 is provided in the tail ofthe flashlight, while the positive pole of the battery 15 is closer tothe front of the flashlight. According to the present invention, aunique method and circuit of powering the control circuit 27 has beendeveloped according to the present invention, taking advantage oftransient effects taking place over a short time when the switch 16 isopened. Opening the switch can also be imagined as making the resistanceof the switch 16 infinite. Due to dynamic effects, the voltage close tothe switch rises for a short time period at the node 31 that is locatedbetween the light emitting diode 18 and the high-frequency switch 16.This transient effect is used for capturing over a short period of timesome electric energy in the form of electric current for charging acapacitor 32. A blocking diode 33 is connected in series in front of thecapacitor 32 so that this current cannot discharge back into the buckconverter circuit 26 via the node 31 after the transient effect hasstopped and the voltage at the node 31 has dropped to a lower level thanthe voltage across the capacitor 32.

After this transient effect is over, the electric energy stored in thecapacitor 32 discharges via a voltage regulator 34. For this voltageregulator 34, a regular linear voltage regulator is acceptable since thecontrol circuit 27 requires only a very minimal current so thatefficiency is not a major concern for the control circuit. The powerconsumption of the control circuit 27 is negligible in comparison to thepower consumption of the buck converter circuit 26. A power line 35leads from an output of the voltage regulator 34 into themicrocontroller 29.

The unique properties of this design allow to eliminate a separate powersupply circuit running from the batteries 15 into the control circuit.This has the consequence that another spring probe can be dispensed withsince instead of a spring probe all that is necessary is to connect thediode 33 at its input side with the barrel of the flashlight. Asillustrated in FIG. 1, the node 31 is in the section where the conductorof the buck converter circuit 26 is the barrel of the flashlight.

Another effect of this unique circuit for capturing electric energy fromtransient effects is a boosting effect. The voltage rises significantlyover the voltage that is provided by the batteries 15. For example, at abattery power of 4.5 V, an output voltage from the capacitor 32 of about15 V can be captured. Again, this is due to dynamic effects that occurover a short time when the resistance of the switch can be imagined tobecome infinite due to opening the switch. In addition, the boost effectis proportional to the duty cycle. As discussed in connection with FIG.1, the duty cycle is increased when the battery voltage drops over time,for instance controlled to be 0.8 at a battery voltage of 4V and 0.58 ata battery voltage of 5.5 V. The following table 2 reflects thiscorrelation:

VBAT Duty Cycle OUTPUT - BUCK (TYP) OUTPUT BOOST 5.5 0.58 3.2 13.15 50.64 3.2 13.89 4.5 0.71 3.2 15.58 4 0.80 3.2 20

As can be seen from table 2, the voltage at the input of the controlcircuit actually rises when the battery voltage drops over time since adecreasing battery voltage means an increased duty cycle.

As a man-machine interface, a pushbutton 36 is provided. This pushbutton36 is provided for turning the flashlight on and off and depending onthe model also for selecting a specific flashlight operational mode, forexample by repeatedly pressing the pushbutton 36 at a particularsequence in time, for instance several pushes within a specific timeperiod. Structurally, the pushbutton 36 can be implemented by a snapdome. For avoiding any leakage of electric current through the controlcircuit, which may for instance result in a very minor though stillvisible powering of the LED 18, the voltage regulator 34 is providedwith an enabling pin 37. The microcontroller feeds a signal through thesignal line 38 to the enabling pin and keeps the voltage regulatorturned on while the microcontroller is in a controlling mode. When theflashlight is turned off, the enabling pin disables the voltageregulator 34, blocking any power through the voltage regulator 34 andtherefore preventing any leakage power that may leak otherwise throughthe control circuit 27 into the buck converter circuit 26.

In the following, the structural design of an exemplary flashlight isdescribed by referring to FIGS. 3 and 4.

FIG. 3 shows a similar side view compared to FIG. 11 demonstrating theprior art. This exemplary flashlight 1 according to the presentinvention generally includes barrel 2, head assembly 3 located at theforward end of barrel 2, and switch and tailcap assembly 4 located atthe rear end of barrel 2. The head assembly 3 is disposed about theforward end of the barrel 2, and the switch and tailcap assembly 4encloses the end of barrel 2.

The barrel 2 may include a textured surface 126 along a portion of itslength for a user to grip. In the present embodiment, textured surface126 may be provided by broaching. Alternatively, textured surface 126may comprise a knurled or machined surface. Any desired pattern may beused for textured surface 126. In this particular design, for texturedsurface, also referred to as knurling, has been manufactured bymachining. Textured surfaces 39 and 40 are provided at the switch andtailcap assembly 4 and the head assembly 3, respectively. In thispreferred embodiment, the textured surface 39 on the switch and tailcapassembly 4 and the textured surface 39 at the head assembly 3 areidentical. The head assembly 3 comprises a substantially plane frontface 41 while also other shapes are used in other preferred embodiments,for instance a scalloped front face for breaking glass in case of anemergency.

FIG. 4 is a partial cross-sectional view of flashlight 1 of FIG. 3 takenalong the plane indicated by line B-B. An LED light source 18 is mountedto the forward end of the barrel 2. Two 3 V batteries 15 areaccommodated within the barrel 2 and connected to each other in seriesso that the total voltage output of the two batteries is 6 V when thebatteries are still fresh. A spacer 42 is provided between the twobatteries 15 having on the one hand the function to facilitateelectrical contact between the positive pole of the battery locatedcloser to the rear of the flashlight and the negative pole of thebattery located closer to the front of the flashlight and on the otherhand protect the batteries from damage caused by stronger impacts sincethe spacer 42 provides for a stronger mechanical support between theouter housing rims of the batteries 15 via the spacer 42 sandwichedtherebetween. In addition to protecting the batteries 15 from damage dueto impacts, the spacer 42 also prevents any interruption in the currentflow that may otherwise result from impacts. It is specificallyimportant to prevent such current flow interruptions in the designaccording to the present invention for keeping the control circuit 27powered and avoid inadvertently turning off the flashlight. In thisconnection, it is referred back to the control circuit 27 shown in FIG.2, demonstrating the enabling pin 37 of the voltage regulator 34, theenabling pin 37 receiving electric voltage through the signal line 38for keeping the voltage regulator 34 on. As discussed in connection withFIG. 2, absent any voltage at the enabling pin 37, the voltage regulator34 is turned off, specifically for avoiding any leakage of currentthrough the control circuit 27 and therefore avoiding any currentflowing through the LED 18. Even a relatively short interruption inreceiving battery power may result in turning the voltage regulator 34off in its entirety, and it could then only be restarted by pressing thepushbutton 36 again for turning the entire flashlight on and selectingthe operational mode. Depending on the selected operational mode, thismight require even multiple button pushes. The spacer 42 effectivelyavoids any interruption in the electric current.

The design of this spacer 42 is shown in FIGS. 5 and 6. An outer rim 46encompasses an open space 47 into which the electric contact 48protrudes. The outer rim of 46 is preferably made from a dielectric suchas electrically non-conductive plastics. The electric contact 48 ispreferably made from metal having both good electrical conductiveproperties, as well as being able to provide sufficient spring force.According to a preferred embodiment, the electric contact 48 can be madefrom steel.

FIG. 6 shows a cross-sectional view taken along lines C-C in FIG. 5. Theelectric contact 48 is sandwiched between an upper rim part 49 and alower rim part 50. The upper and lower rim parts 49 and 50 can beattached to each other by gluing. As it becomes apparent from FIG. 6,the electric contact 48 is kept in place by abutting against an innercylindrical surface 51 if moved in a radial direction, and can thereforenot be removed in this direction when sandwiched between the upper rimpart 49 and lower rim part 50.

Returning now to the sectional view of the entire flashlight accordingto FIG. 4, the switch and tailcap assembly 4 comprises a circuit board 8holding the control circuit 27 for controlling the power supply to thelight source, in this exemplary embodiment designed as an LED 18, andalso for controlling various modes of operation for the flashlight ifthe specific flashlight is designed as a multi-mode flashlight. Thevarious operational modes of the flashlight will be explained furtherbelow by referring to FIGS. 7-10 showing flow diagrams demonstrating howthese multiple operational modes can be established by multiple pusheson the pushbutton 36. The pushbutton 36 interacts with a snap dome 52and creates an electrical contact between contacts provided on thecircuit board 8. For protecting the pushbutton assembly and also forsealing the tail end of the flashlight, a switch port seal 53 isprovided that interacts via its outer rim 54 with an outer tailcaphousing 55 in a sealing fashion. The outer tailcap housing 55encompasses an inner tailcap housing 56 that is preferably made from adielectric, for instance made from plastic by injection molding. Thetailcap housing 56 accommodates a spring probe 57 comprising a spring 58and a pin 24. At its tail end, the spring probe 57 is in electriccontact with the circuit board 8 and at its front end via the pin 24with the negative pole of the batteries 15. The circuit board 8 isfurther in electric contact with the outer tailcap housing 55 thatestablishes via a ring-shaped circumferential contact surface 60 anelectrical contact with a respective ring-shaped end face 61 of thebarrel 2.

The switch and tailcap assembly 4 comprises at its front end an externalthread 62 that is threaded into an internal thread 63 provided at thetail end of the barrel 2. A lip seal 64 seals the switch and tailcapassembly 4 with respect to the barrel 2. Although it would be possibleto establish an electrical contact between the outer tailcap housing 55and the barrel via the internal and external threads, respectively, froma manufacturing point of view it is preferred to establish the electriccontact between the contact surface 60 and 61 so that the surface of theentire barrel 2 and the outer tailcap housing 55 can be covered by anappropriate surface coating or surface treatment such as applying paint,enameling or anodizing including the threads. The contact surfaces 60and 61 can then easily be machined so that any coating is removed inthis area where the electric contact should be established, creatingwell defined plain contact surfaces 60 and 61. In addition, since thesecontact surfaces 60 and 61 are pressed against each other by the forcecreated from the threads 62 and 63, a good electric contact of lowresistance can be established.

Briefly summarizing the switch and tailcap assembly 4 again, itcomprises a very simple design requiring only two electric contacts,namely a first electric contact established by the spring probe 57between the negative pole of the battery 15 and the circuit board 8, anda second electric contact established via the contact surfaces 60 and 61via the outer tailcap housing 55 with the electric circuit board 8. Thelatter contact is connected via the LED 18 with the positive pole of thebattery 15 that is located closer to the font of the barrel 2, as willbe discussed in the following by describing the head assembly and theassembly provided within the front end of the barrel 2. The circuitboard 8 comprises the control circuit 27 and the high frequency switch16 as well as the resistor 23, all described in FIG. 2 and summarized asforming together with the pin 24 the tail circuit section 22 asindicated in FIG. 1. The batteries 15 and the barrel 2 jointly form thebarrel circuit section 21 as likewise indicated in FIG. 1.

In the following, the structural implementation of the head circuitsection 20 (see FIG. 1) is described. The LED 18 is held in a lightsource carrier 59, including also the necessary circuit parts forpowering the LED 18, including the inductor 17 and the blocking diode 19of the head circuit assembly 20 as demonstrated in FIGS. 1 and 2. Anelectric contact 65 contacts the positive pole of the battery 15. Anelectric conductor 66 establishes an electric contact from the lightemitting diode 2 to a crown-shaped LED carrier 67 comprising at its rearend an external thread 68 that is screwed into an internal thread 69provided in the front of the barrel 2. The LED carrier 67 comprises aflange 70 pressing against a front face 71 of the barrel 2 when theexternal threads are screwed into the internal threads 69 of the barrel2, establishing an electric contact between the flange 70 and thering-shaped front face 71 of the barrel 2. Like the ring-shaped end face61 also the ring-shaped front face 71 can be machined to establish aplane and even contact surface that is free of any coating so that thegood electric contact can be established when the LED carrier 67 isscrewed firmly into the front of the barrel 2. The LED carrier 67 may befree of any coating in its entirety since it is just an internalflashlight part that can be manufactured by any standard manufacturingmethod such as stamping, extruding, turning and/or milling or anycombinations thereof.

In addition, this LED carrier 67 also provides an external thread 72onto which the internal thread 73 of the head assembly 3 can be screwed.The head assembly 3 can be designed to be free of any circuit parts, andprovide just optical functions such as to focus, collimate or dispersethe light from the LED 18 via a parabolic reflector 74 and to send thelight out through a lens 75 sealing the head assembly 3. The relativeposition between the reflector 74 and the LED 18 can further be changedby screwing the head assembly away from or towards the LED 18, changingthe focal point.

In the following, the structural implementation of the electric circuitaccording to the present invention as demonstrated in FIGS. 1 and 2 isdescribed. The two batteries 15 are connected in series via the spacer42 described in FIGS. 5 and 6 and are connected to the head circuitsection 20 via the contact 65, allowing electric current to flow throughthe LED 18. From the outlet of the LED 18, electric current flows intothe LED carrier 67 and via the flange 70 and contact surface 71 into thebarrel 2. From the barrel 2, electric current flows via the contactsurfaces 60 and 61 and the outer tailcap housing 55 into the circuitboard 8 and from the circuit board 8 via the spring probe 57 comprisingthe spring 58 and the pin 24 into the negative pole of the battery 15,closing the electric circuit. The control circuit 27 as well as the highfrequency switch 16 and the resistor 23 are implemented on the circuitboard 8.

A variation of this embodiment can be created by providing both the buckcircuit 26 and the control circuit 27 in the front of the flashlight andprovide another very simple control circuit in the tail of theflashlight that controls just the on/off functions as described above.This would still allow a structurally simple design comprising only onesingle spring probe, namely the spring probe in the tail of theflashlight contacting the negative pole of the battery 15. In thisalternative design, the LED could be in the head of the flashlight witha current regulating circuit located also in the head. The tailcap wouldstill have a microcontroller, but would be provided only for shuttingthe flashlight on and off and selecting the operational mode of theflashlight, i.e. just perform the functions of the user interface, butnot the function of regulating the current. The tailcap would no longerhave any control over the LED current (either directly or indirectly),but would be an electronic switch that controls on/off. While thisalternative design would still have only one single spring probe, itwould have an extra control circuit controlling on/off and modeselection. It is therefore preferred to have only one control circuit inthe tail of the flashlight that is also accessed by the user interface,in this case the pushbutton.

While a variety of different designs for user interfaces are possible,for instance comprising one or more pushbuttons, a GPS device sensingthe motion of the entire flashlight, both translatory and/or rotationalmovement, or a sensor measuring acceleration, in the following onepreferred example of a user interface is described by referring to FIGS.7 to 10. This exemplary user interface is designed to be as simple aspossible, allowing three operational modes, namely 1. a momentary mode,2. a latch mode; and 3. a strobe mode. All of these modes are selectedby the user simply by pushing the pushbutton 36 (see FIG. 4) one or moretimes. The operation starts at 76 with the flashlight turned off. Onepush of the pushbutton 36 results in selecting the momentary mode at 77.This operational mode can be changed, for instance, by pressing thepushbutton 36 a second time within a short time period, resulting inestablishing the latch mode at 79. By an additional input at 80, forinstance, by pushing the pushbutton again after a short time period,finally at 81 a strobe mode can be established. It is to be understoodthat an unlimited number of additional modes can be established, forinstance by pressing the pushbutton 36 at a short sequence in time forone or more times.

FIG. 8a goes into more detail as to how the momentary mode isestablished. If the user chose at 82 to establish the momentary mode thelight is enabled at 83. Referring briefly back to FIG. 2, enabling thelight means that the microcontroller 29 keeps sending a signal throughthe signal line 38 to the enabling pin 37 of the voltage controller 34.At 84, it is determined whether the button has meanwhile been released.If not, the light is kept in the enabled state. If the pushbutton hadmeanwhile been released, it is determined at 85 whether the pushbuttonwas pressed for more than 250 ms. If that is the case, the light isdisabled at 86 and the flashlight is turned off at 87. If the pushbuttonwas not pressed for more than 250 ms, it is determined at 88 whether thepushbutton is pushed again, and if so, a mode change is activated at 89,in this case moving to the next operational mode in the sequence ofoperational modes which is the latch mode in which the flashlight iskept turned on permanently. If in contrast the pushbutton was not pushedagain after a short time period, i.e. had been released for longer than250 ms, this is determined at 90 and the control loop moves on todisable the light at 86 and then again turn off the flashlight entirelyat 87. This latter routine means that the flashlight was still operatedin the momentary mode, but only for a very short time period of up to250 ms, but no mode change was activated since the pushbutton was notpressed for a second time.

While FIG. 8a demonstrates the actions of the user for selectingoperational modes and how the actions by the user are perceived by thecontrol, FIG. 8b demonstrates the current regulation starting from themomentary mode. At 91, the current regulation for the momentary mode isstarted. When the light is enabled as determined at 92, the pulse widthmodulation is regulated at 93 to set the current to 1 Amp. Again,modulating the pulse width means adjusting the duty cycle as this hasbeen explained in detail in connection with FIGS. 1 and 2. If it isdetermined at 94 that the light is still enabled, which does of coursedepend on the actions by the user, the control loop keeps controllingthe battery current to remain at 1 Amp. If in contrast it is determinedat 94 that the light is disabled or in other words not enabled, thepulse width modulation is disabled and the LED and respectively theentire flashlight is turned off at 95, again meaning as described inconnection with FIG. 2 to disable the voltage regulator 34 via disablingthe enabling pin 37.

FIG. 9a demonstrates the user action starting from the latch mode at 96.If the pushbutton is still pressed, no change will happen. If it isdetermined though at 97 that the pushbutton has been released, it isdetermined at 98 whether the pushbutton has been held for more than 250ms. If so, this means that the latch mode is still established. If it isdetermined at 99 that the pushbutton is not pushed, the latch mode ismaintained, i.e. the flashlight is kept on permanently. For example,this would relate to turning the flashlight permanently on and then justholding it at the barrel or placing it somewhere, for instance on thetable. However, if the pushbutton is pushed, it is determined at 100whether it has meanwhile been released. If the pushbutton is pushed,still no change happens, i.e. the flashlight is kept on in its permanentstate. Only when the pushbutton is finally released at 101, the light isdisabled and the flashlight is finally turned off at 102.

Going back to 98, if it is determined that the pushbutton was heldlonger than 250 ms before it had been released, it is determined at 103whether the pushbutton is pushed again, and if such repeated pushinghappened within 250 ms, another mode change is activated, namely a modechange into the strobe mode at 104. However, if it is determined in 105the pushbutton was released for longer than 250 ms prior to pushing itagain the control routine goes back to 99, meaning that no mode changeinto a different mode is activated. Summarizing the control, modechanges only happen if the pushbutton is pressed repeatedly within ashort time period of less than 250 ms. If it is determined that thepushbutton was released for more than 250 ms, the control system decidesthat the mode that had been established prior to pushing the pushbuttonagain after a release time that exceeds 250 ms was intended to beselected. By subsequently pushing the pushbutton again after a longerrelease period the system perceives this button push as the user'sintent to shut down the flashlight.

As far as the current regulation for the latch mode as shown in FIG. 9bis concerned, it looks very similar to the current regulation for themomentary mode as shown in FIG. 8b . At 106, the current regulation forthe latch mode is started. When the light is enabled as determined at107, the pulse width modulation is regulated at 108 to set the currentto 1 Amp. Again, modulating the pulse width means adjusting the dutycycle as this has been explained in detail in connection with FIGS. 1and 2. If it is determined at 109 that the light is still enabled, whichdoes of course depend on the actions by the user, the control loop keepscontrolling the battery current to remain at 1 Amp. If in contrast it isdetermined at 109 that the light is disabled or in other words notenabled, the pulse width modulation is disabled and the LED andrespectively the entire flashlight is turned off at 110, again meaningas described in connection with FIG. 2 to disable the voltage regulator34 via disabling the enabling pin 37.

FIG. 10a demonstrates the user action when starting from the strobe modeat 111. Since this embodiment only comprises three different operationalmodes and the strobe mode is the last in the sequence, a user actiondoes not result in establishing another operational mode so that thecontrol routine depending on the user action is relatively short. If itis determined at 112 that the pushbutton is released and at 113 that ithas not been pushed again, the strobe mode is maintained. Even if thepushbutton has been pushed again at 113 and is kept pushed, the strobemode is maintained. Only if it is determined at 114 that the pushbuttonhas again been released, this signals to the flashlight that the userintends to turn it off so that the light is disabled at 115 and theflashlight is finally turned off at 116.

As far as the control of the current in the electric circuit isconcerned, the control routine is more complex than for the momentaryand the latch mode as shown in FIGS. 8b and 9b , respectively. Startingthe strobe mode battery current regulation at 117, if it is determinedat 118 that the light is enabled, a timer is set to zero at 119. At 120the pulse width modulation regulates the battery current to 1 Amp andkeeps it at that current for 53 ms until it is determined at 121 that 53ms are exceeded so that the battery current is regulated at 122 to 0.01Amp. The reason why a minor current is still maintained correlates tothe unique design of the control circuit as described in connection withFIG. 2 above. The control circuit always needs to be provided with alittle power, even though it might be just marginal as needed forkeeping the microcontroller 29 working. Even though this has the sideeffect that the LED is not turned off entirely, the light emitted by theLED in this stage is so little that it is not perceived by the viewer,in particular after the user has perceived the much brighter lightresulting from the 100 times higher current of 1 Amp when the strobelight is in its full power phase.

If it is determined at 123 that the timer has reached 67 ms from thetime it was set to zero at 119, the control routine moves on todetermine at 124 whether the light is still enabled, in other wordswhether the user has not meanwhile turned off the light, and if stillenabled, jumps back in the control routine to 119 where the timer is setto zero and repeats this control routine for turning the lightperiodically on at full power and subsequently turning it close to offto complete one blinking cycle. When it is finally determined that thelight is disabled, i.e. the user has pushed the pushbutton again to turnthe flashlight off, the pulse width modulation is disabled at 125 andthe LED and the entire flashlight are finally turned off at 125.

What is claimed is:
 1. A flashlight having a head section with at leastone light emitting diode (“LED”) for emitting light from the headsection, a tail section with a man-machine interface and a barrel whichholds a portable DC power source having a positive pole and a negativepole, said barrel being located between the head section and the tailsection, said positive pole being located more proximate to the headsection than the negative pole, comprising: a buck converter circuitcomprised of: a head circuit section including the at least one LED andan inductor; a barrel circuit section including the portable DC powersource; and a tail circuit section including a high frequency switch;and a control circuit that interacts with the buck converter circuit tocontrol current flowing through the at least one LED; wherein thecontrol circuit is powered by a transient effect created at a nodelocated between the at least one LED and the high frequency switch whenthe high frequency switch is opened.
 2. The flashlight of claim 1,wherein the transient effect is a voltage rise for a short period oftime at the node.
 3. The flashlight of claim 2, wherein the transienteffect is used to charge a capacitor.
 4. The flashlight of claim 3,wherein a blocking diode is located in series between the capacitor andthe node.
 5. The flashlight of claim 2, wherein the control circuit doesnot require a separate power circuit form the portable DC power sourceto power said control circuit.
 6. The flashlight of claim 1, wherein thevoltage rise creates a boosting effect in which the voltage rise is at asecond voltage that is greater than a first voltage provided by theportable DC power source.
 7. The flashlight of claim 6, wherein theboosting effect is proportional to a duty cycle of the high frequencyswitch.
 8. The flashlight of claim 6, wherein the second voltage risesas the first voltage drops.
 9. The flashlight of claim 1, wherein theman-machine interface is configured to allow a user to select from aplurality of modes of operation of the flashlight.
 10. A circuit forproviding power to a control circuit which interacts with a buckconverter circuit which includes a portable DC power source, a lightemitting diode (“LED”) and a high frequency switch, wherein the controlcircuit controls current flowing through the LED, comprising: acapacitor electrically connected in series to a node, said node beinglocated in series between the LED and the high frequency switch; and ablocking diode located in series between the capacitor and the node;wherein the control circuit is powered by a transient effect created atthe node when the high frequency switch is opened.
 11. The circuit ofclaim 10, wherein the control circuit does not require a separate powercircuit form the portable DC power source to power said control circuit.12. The circuit of claim 11, wherein the transient effect is a boostingeffect in which there is a second voltage at the node which is higherthan a first voltage provided by the portable DC power source.
 13. Thecircuit of claim 12, wherein the boosting effect is proportional to aduty cycle of the high frequency switch.
 14. A circuit for providingpower to a control circuit which interacts with a buck converter circuitwhich includes a portable DC power source, a light emitting diode(“LED”) and a high frequency switch, wherein the control circuitcontrols current flowing through the LED, comprising: a first electricalnode located in series between the LED and the high frequency switch;and a capacitor connected at a second node; wherein the capacitor iselectrically connected in parallel to the first node by means of ablocking diode located in series between the first electrical node andthe capacitor at the second node; and wherein the control circuit ispowered by energy stored in the capacitor during a transient effectcreated at the first node when the high frequency switch is opened. 15.The circuit of claim 14, wherein the control circuit does not require aseparate power circuit form the portable DC power source to power saidcontrol circuit.
 16. The circuit of claim 15, wherein the transienteffect is a boosting effect in which there is a second voltage at thenode which is higher than a first voltage provided by the portable DCpower source.
 17. The circuit of claim 16, wherein the boosting effectis proportional to a duty cycle of the high frequency switch.